Impregnating the wood, while in a vacuum, with a strong solution of sulphate of iron, and afterwards forcing into the timber a solution of sulphate of lime or any of the alkaline carbonates, such as carbonate of soda, by which means the oxide of iron becomes insoluble. The wood is also rendered incombustible by this process.
Two conditions of construction are necessary to preserve timber from decay - (1) continual access of a free current of air, by provision of proper ventilation; (2) the assured exclusion of wet from without. Neither damp nor dry-rot will readily attack timber which is so placed and protected. What most rapidly destroys timber is the alternation of wetting and drying; the next most frequent cause of decay is the generation of fungus by reason of total atmospheric stagnation. Another point of some importance is to avoid seating timber (such as wall-plates, joists, girders, breastsummers, etc.) in or. abutting immediately upon masonry or brickwork which is being laid with Portland cement. Immediately next to all such faces or butt-ends of timber, the work should be laid with mortar made of 1 part (by weight) ground quicklime and 3 parts cleanly-sifted very dry and ground coal cinders; indeed, it is best to have the lime and cinders ground together, so that they are perfectly blended: but it is indispensable to use this material at once, as it soon slakes from the action of moisture in the air. No dressing whatever will preserve timber as to which the foregoing precautions are neglected.
It is, nevertheless, a good plan - in having a care on these points - to thoroughly dress internal timbers, such as girders, joists, wall-plates, rafters, window and door frames, etc., with a strong solution of carbolic acid before building them in. In sinking timber, as posts, in strong argillaceous soils, charring the heels to a height about 6 in. above-ground - and all spurs as well - is the only means of averting very prompt decay - unless it be by the costly precaution of seating the heels within pottery pipes of sufficient calibre, and filling in with smoking ground quicklime concrete mixed with crushed burnt stone.
The reports from the German and Austro-Hungarian railroads, where the ties used are mostly of oak, pine, fir, and beech, and nearly one-half of the total number in use have been subjected to antiseptic treatment according to various systems, show a reported increase in their average life over and above the average life of untreated ties, as follows: - Oak, 6 years; fir, 7; pine, 9; and beech, 9.
In an interesting paper on " House-rot " (dry and wet rot), Pudil, clerk of works to Prince Lobkovic at Bilin, states, as the result of many years' personal observation, that the rot is always more prevalent on gneiss and granitic sites, and where the soil and building materials are derived from gneiss, granite, or such like rocks, which contain a large proportion of felspar. Not only does the alkali appear to afford nutriment to the fungi, but these stones and the soils derived from them are highly hygroscopic, and occasion a certain dampness in the surroundings, which favours the development of these growths. Dr. Leube has shown that 100 parts of the said fungi, dried at a temperature of 212° F. (100° C), gave on analysis 30.55 carbonic acid, 4.06 hydrogen, 29.92 oxygen, 2.46 nitrogen, 32.98 ash; the ash containing potash, soda, magnesia, lime, clay, iron, manganese, chlorine, sulphuric acid, carbonic acid, and silicic acid. Sound timber of the same description as that from which the fungi were taken, gave 1 per cent, of ash only.
The enormously increased proportion of ash shows how largely the fungus draws upon the surrounding masonry for nutriment. (N. D. Ge-werbe Zeit.)
The durability of wood depends on several circumstances, some being inherent to the wood itself, others owing to outward conditions. Woody fibre, by itself, is very little affected by air or water, but several other principles may be present in wood which, by entering into decomposition, induce a similar state in the woody fibre. Such are albumen, etc, which exist in the sap. Resinous bodies, by preventing the absorption of water, and by being distasteful to most insects, act as preservatives; hence, most naturally, resinous woods are durable. The heart-wood of trees is less liable to attacks from insects than the outer or splint-wood. Dry wood is also but little liable to such attacks. Young sappy wood, on the other hand, is specially prone to attacks from insects. Trees grown in cold climates and in poor soils produce wood which is, as a rule, more durable than that obtained from similar trees grown in a warmer, richer, and moister soil. Wood felled in winter is more durable than that felled in the spring or summer, probably owing to the sap not being so abundant at the former epoch. Wood placed in warm and moist situations, especially if light and air be excluded, is more liable to decay than when placed in dry, cool, and airy positions.
Moisture and a close atmosphere favour the growth of peculiar fungi on the wood, which eventually favour the decomposition of the fibres and the disintegration of the mass. These fungi are generally the Thetephora domestica, the Boletus destructor, and the Cerulins vastator. A remedy for the ravages effected by these fungoid growths is found in the repeated application of acetate of iron made from wood vinegar.
As the sap is such an active agent in the rapid decay of wood, any means by which its removal can be effected, even if only partially, will conduce much to the preservation of the wood. Soaking in cold water, boiling in water, steaming in close vessels, have all been tried, and found effective under certain circumstances. Drying and charring the external portions have also been found efficacious. To this end the wood is immersed or painted over with tar, creosote, or similar bodies, after being well kiln-dried; the tar is then lighted and allowed to char the wood superficially. When extinguished, it may again be tarred. By causing the root end of a freshly-felled tree to stand in a solution of sulphate of iron, bichloride of mercury, sulphate of copper, etc, these bodies are sucked up into the wood, and replace the sap. This method seems to be the one which gives the most promising results, and wood treated in this manner with sulphate of iron becomes extremely durable. (Eng. Mech.) Inquiries into the causes of decay of timber prepared with copper salts have been made by H. Rottier, of the University of Ghent. The disappearance of the copper-sulphate may be accounted for by the presence of (1) iron, (2) certain solutions, (3) carbonic acid.